The concept of a quasi-particle excitation in an interacting many-body system will be discussed from both the physical and the math e matical points of vi e w.Th e physi cal origin of mass enhancement, wave fun ction re normalization, interac tio ns betwee n quasi-particles, etc. will be presented.Landau's Fermi liquid theory, including th e quasi-particle kinetic equation, will be reviewed.Finally, the domain of validity of the quasi-particl e approximation will be discuss ed.

Journal of Research of the National Bureau of Standards Section A Physics and ChemistryJul 1, 19706 citations

arXiv:hep-th/0409049 · Journal of High Energy Physics

Quasi-particle re-summation and integral gap equation in thermal field theory

André LeClair

Published May 31, 2005• 5 citations

arXiv HTML PDF

DOI: 10.1088/1126-6708/2005/05/068

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Thermally activated detection of dark particles in a weakly coupled quantum Ising ladder

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The ${\mathrm{Ising}}_{h}^{2}$ integrable field theory emerges when two quantum critical Ising chains are weakly coupled. This theory possesses eight types of relativistic particles, among which the lightest one ( ${B}_{1}$ ) has been predicted to be a dark particle, which cannot be excited from the ground state through (quasi)local operations. The stability on the one hand highlights its potential for applications, and on the other hand makes it challenging to be observed. Here, we point out that the mass of the ${B}_{1}$ dark particle ${m}_{{B}_{1}}$ appears as a thermally activated gap extracted from local spin dynamical structure factors at low frequency ($\ensuremath{\omega}\ensuremath{\ll}{m}_{{B}_{1}}$) and low temperatures ($T\ensuremath{\ll}{m}_{{B}_{1}}$). We then further propose that this gapped behavior can be directly detected via the NMR relaxation rate measurement in a proper experimental setup. Our results provide a practical criterion for verifying the existence of dark particles.The ${\mathrm{Ising}}_{h}^{2}$ integrable field theory emerges when two quantum critical Ising chains are weakly coupled. This theory possesses eight types of relativistic particles, among which the lightest one (${B}_{1}$) has been predicted to be a dark particle, which cannot be excited from the ground state through (quasi)local operations. The stability on the one hand highlights its potential for applications, and on the other hand makes it challenging to be observed. Here, we point out that the mass of the ${B}_{1}$ dark particle ${m}_{{B}_{1}}$ appears as a thermally activated gap extracted from local spin dynamical structure factors at low frequency ($\ensuremath{\omega}\ensuremath{\ll}{m}_{{B}_{1}}$) and low temperatures ($T\ensuremath{\ll}{m}_{{B}_{1}}$). We then further propose that this gapped behavior can be directly detected via the NMR relaxation rate measurement in a proper experimental setup. Our results provide a practical criterion for verifying the existence of dark particles.

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What is a quasi-particle?

J. R. Schrieffer

Journal of Research of the National Bureau of Standards Section A Physics and ChemistryJul 1, 19706 citations

The

{\mathrm{Ising}}_{h}^{2}

integrable field theory emerges when two quantum critical Ising chains are weakly coupled. This theory possesses eight types of relativistic particles, among which the lightest one (

{B}_{1}

) has been predicted to be a dark particle, which cannot be excited from the ground state through (quasi)local operations. The stability on the one hand highlights its potential for applications, and on the other hand makes it challenging to be observed. Here, we point out that the mass of the

{B}_{1}

dark particle

{m}_{{B}_{1}}

appears as a thermally activated gap extracted from local spin dynamical structure factors at low frequency ($\ensuremath{\omega}\ensuremath{\ll}{m}_{{B}_{1}}$) and low temperatures ($T\ensuremath{\ll}{m}_{{B}_{1}}$). We then further propose that this gapped behavior can be directly detected via the NMR relaxation rate measurement in a proper experimental setup. Our results provide a practical criterion for verifying the existence of dark particles.